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Old school design methods

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Old school design methods

Old 5th Jun 2013, 22:11
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Old school design methods

Hi everyone,

This question has really been bugging me for ages so I may as well try and ask it.

Before the advent of CAD I can understand how the designers/engineers of plane could come up with 3 view sketches (front side and top) but what I don't understand is how they came up with wing rib drawings or fuselage frames, that would fit the design at any point in the wing or fuselage?

http://www.seqair.com/Falco/Kits/Kit302/Kit302.gif

How did they decide the measurements and where frames such as this would be placed?

Thank you very much
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Old 5th Jun 2013, 22:19
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Come on now, give us a break...look at all of the stuff designed before cad...

If you have the fuselage or wing profile, you can get the measurements for the ribs at any point...all you need is some graph paper...


Last edited by FlightPathOBN; 5th Jun 2013 at 22:19.
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Old 5th Jun 2013, 22:24
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How could I have missed wing profiles! apologies for that, what about the fuselage profiles since the shape is drastically changing?
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Old 5th Jun 2013, 22:39
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Basically the drawing board is your tool, you work from initial aerodynamic shapes, and construct the aeroplane on paper, on a series of sheets of paper - the bigger the better. Working in 3-view, you put faint working lines across that allow you to join everything up. It is reliant upon having a good and continuously developing mental picture of the aeroplane or component you're designing.

I worked for a while in the drawing office(s) at RAE where I did a fair bit of this in the latter days of pencil designing when CAD was starting to become new - and happily designed quite a lot of complex shapes.

Genghis Sr. was for rather longer in the Vickers Armstrong drawing office at South Marston where he worked on wing sections for aeroplanes like the Attacker and Scimitar. Comparing notes with him from time to time, his tasks were similar - but those chaps were very good engineers, with an excellent mental picture of what they were designing. Also however they had A LOT of people - think large rooms full of drawing boards, full of intense young men with thick framed glasses, slide rules and collections of data books and drawing instruments on the side table. The amount of training they had, and the level of skill in the task, was arguably rather greater than many CAD operators nowadays.

Mike Whittaker, who's still out there designing using CAD these days, designed his earlier designs just this way - (Plans | MW Club if you'd like a set to look at) and he'll send you a complete set of drawings for any of his designs. I used to use them for teaching aircraft design when that was my job and very good they were too.

Last edited by Genghis the Engineer; 5th Jun 2013 at 22:44.
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Old 5th Jun 2013, 23:37
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Does anyone remember the wonderful Jeffries drawings in Air Trails magazine?

After an excellent landing etc...
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Old 6th Jun 2013, 02:29
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I don't understand is how they came up with wing rib drawings or fuselage frames, that would fit the design at any point in the wing or fuselage
It's done by a process known as "lofting". Originated in ship building. Google "aircraft lofting". A primer

http://www.dept.aoe.vt.edu/~mason/Ma...GeomIssues.pdf
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Old 6th Jun 2013, 04:31
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I was around in the days of the Attacker, Swift and Scimitar and remember that a full size wooden mock-up of the later was in the 'sheds' at Hursley (near Winchester). To reach this mock-up, draftsman had to negotiate a lengthy walk across a field of nettles armed with a ruler to take measurements and then go back to their drawing-boards and create the 3 view drawing.
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Old 6th Jun 2013, 04:49
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Lofting classes are still available in many boatbuilding schools.
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Old 6th Jun 2013, 07:37
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Slightly off thread
Most of the conventional instrument approach procedures (ILS, VOR, NDB etc.) that you fly Now were designed using only pencil, ruler, tracing paper and a calculator
No CAD
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Old 6th Jun 2013, 08:11
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rennaps.

A calculator????

Slide rule I think!!!!

I never could get the hang of moving the decimal point every time you moved from one end to the other.
I used to do an approximation of the result on paper to get the decimal point right.
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Old 6th Jun 2013, 12:07
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Originally Posted by Genghis the Engineer
teaching aircraft design when that was my job
Welcome coming back from Banningland! Future is behind us.

Time is not compressible in Insurance and hazard and Air safety is not solvable in stats..
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Old 6th Jun 2013, 12:26
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Thanks for some good info - I remember the drawing offices at my old work filled with lots of boards and hard working men and women. No computers ;-)

My impression is that the CAD tools sometimes separate us from the reality of design. The old designers may not have had the fancy software, but they had a lot of common sense behind them. I battle daily with young engineers who will blindly believe the numbers that the computer spits out.

A few recent gems:
"I don't care what the flight test results say, my prediction is correct. I looked up the formula in Roskam and I've double checked my maths!"

"OK, so we designed to the finite element predictions, and the finite element overpredicted the stresses by 50%. At least we know the structure is strong enough".
"Yes, but it's overweight"
"And the problem is??"

"But the diagonal tension field didn't show up on NASTRAN, how am I meant to know about it? "

Children of Magenta?
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Old 6th Jun 2013, 13:40
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I used to do an approximation of the result on paper to get the decimal point right.

which is why all us olde phart engineers have difficulty with the youngsters who believe their computer output garbage without doing a back of a fag packet sanity check rough calc ...

Slide rule I think

I can't recall a single occasion where my slide rule stopped working because of battery problems ... and, for many calculations, its accuracy is just as practical as the 495 irrelevant decimals which the computer spits out.

stressmerchant, I'm with you good sir.

Even in more recent times old techniques die hard. Jess Smith, who was the force behind the short lived MAMBA single in Melbourne started the design in chalk on his hangar floor ..
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Old 6th Jun 2013, 16:54
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It's done by a process known as "lofting". Originated in ship building
after my apprenticeship at RR i went into the aerodynamic fairings Design office, where i learned to loft engine fairings and doors and pylons etc.

we used to draw on sheets of nice shiny aluminium with lots of french curves and trammels, with erasing done by emery cloth, these lofts were scale 1:1 and were taken up to Hucknall to be carefully cut out to make egg box molds, from which tooling was made to profile aluminium sheets. being rascals we used to put the shiny aluminium off cuts on the floor when the tea trolley came around we played guess what colour

also believe it had something to do with parachute packing on long tables which were in a loft as it was the only space long enough for these tables.

we used to draw in ink on finest Irish linen which could have the starch soaked out to make cracking hankeys and dusters. i still shake my pencil when drawing as a throw back to getting the ink flowing in the old pen knibs.

with regards to the bits between the sections, we used to rely on the toolmakers eye to blend it all in nicely, which CAD does for us now.

The problem is nowadays that people forget that the computer is just a tool of the job, as was the drawing board.

and in some cases the limitations of the tools or the operators can influence the design solution rather than looking for another tool, like the one in your head.

CAD is great though and using virtual reality CAD to see if you can close an engine door latch without lying down is a real step forwards in terms of designed in safety .

Last edited by Bye; 6th Jun 2013 at 16:57.
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Old 6th Jun 2013, 18:33
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Originally Posted by stressmerchant View Post
Thanks for some good info - I remember the drawing offices at my old work filled with lots of boards and hard working men and women. No computers ;-)

My impression is that the CAD tools sometimes separate us from the reality of design. The old designers may not have had the fancy software, but they had a lot of common sense behind them. I battle daily with young engineers who will blindly believe the numbers that the computer spits out.

A few recent gems:
"I don't care what the flight test results say, my prediction is correct. I looked up the formula in Roskam and I've double checked my maths!"

"OK, so we designed to the finite element predictions, and the finite element overpredicted the stresses by 50%. At least we know the structure is strong enough".
"Yes, but it's overweight"
"And the problem is??"

"But the diagonal tension field didn't show up on NASTRAN, how am I meant to know about it? "

Children of Magenta?
Anybody else ever come across a dH era structures professor called Dennis Mead at Southampton? I recall him once saying in a lecture "The trouble with aerodynamicists is that the can assume absolutely anything, except for responsibility".

When I ran an airworthiness office I was often presented with elaborate FE predictions built upon sand. If all else fails, my standard response was "thanks, that's given me confidence that we can now go and build and test a sample structure to destruction on your budget".

The other classic quote there was "The difference between theory and practice? In theory it's right, in practice it isn't."
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Old 6th Jun 2013, 19:02
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I seem to remember my days in the drawing office where I believe we used design criteria laid down years before by the Royal Aircraft Establishment at Farnborough pre WW1.
That is probably why we here in the UK we ended up using proper nuts and bolts instead of self tapping screws like the USA and of course the increased weight and complexity.
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Old 7th Jun 2013, 05:55
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Anybody else ever come across a dH era structures professor called Dennis Mead at Southampton? I recall him once saying in a lecture "The trouble with aerodynamicists is that the can assume absolutely anything, except for responsibility".
Never came across the guy, but for many years I was an aerodynamicist regularly treated to that remark. Then I got a position where I had to oversee the work of the stress office as well as aerodynamics, and guess what - the stressmen made even bigger assumptions. Yes I know they had to sign off on the drawings, but so did the aerodynamicists
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Old 7th Jun 2013, 10:27
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This pic was taken quite some years before John and I started but very similar to our design office. Loft table was in a separate room. http://www.ctie.monash.edu.au/hargra...DESOF_1000.JPG

Actually, I do recall some slide-rule energy failures.

Owain, I experienced the same.

Last edited by djpil; 7th Jun 2013 at 10:28.
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Old 7th Jun 2013, 11:52
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nice photo. our lofting tables were about 50 ft x 20 ft wide.

it was shoes off and get up and on it, with old jumpers taped around knees.
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Old 7th Jun 2013, 12:22
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Actually, I do recall some slide-rule energy failures

.. all mine were after long lunches down at Port Melbourne .. Wriggles used to get quite huffy at my postprandial nodding off.

Strange about one's physical failings ... been a problem all my life .. I had a reputation for nodding off in the cockpit and the boys at work make jokes at my expense on the subject ..
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